1. Field of the Invention
This invention relates to high-power pulsed chemical HF or DF lasers (PCL) and, more specifically, to solid grain pure fluorine gas geneators therefor.
2. Description of the Prior Art
In a PCL, molecular fluorine is dissociated by an energy source, such as flash photolysis or an electron beam, into atomic fluorine ##STR1## which then reacts with either H.sub.2 or D.sub.2 to produce the lasing species vibrationally excited HF* or DF*. ##STR2## Since elemental fluorine has a low boiling point of -188.degree. C., it is usually stored either as a liquid at cryogenic temperatures or as a gas under high pressure. Both storage modes present great safety hazards and logistics problems, and therefore are unacceptable for military and space applications. In view of these problems solid grain fluorine gas generators are highly desirable. Such systems are composed of storable solids which are capable of generating gaseous fluorine on demand. Depending on the nature of the chemical laser, additional constraints are imposed on these generators. For example, a PCL is best operated in a gas recirculation mode at atmospheric pressure using He as a diluent and a fourfold excess of fluorine with respect to H.sub.2 or D.sub.2. Such a PCL requires a pure fluorine gas generator because any gaseous by-products would build up in the recirculating gas with an increase in the number of cycles, and because other fluorine sources, such as NF.sub.3, are not efficiently dissociated by flashlamps, and their reaction rates with D.sub.2 are too slow.
All the solid grain fluorine gas generators developed up to this point are for continuous wave single pass HF-DF lasers and are based on the thermal decomposition of NF.sub.4.sup.+ salts, as described in U.S. Pat. Nos. 3,963,542 and 4,172,884. These generators produce about equimolar amounts of F.sub.2 and NF.sub.3, and therefore cannot be used in a PCL, particularly when operated in a gas recirculation mode. Several systems capable of generating pure fluorine have previously been reported, but have either been refuted or exhibit serious drawbacks, as shown by the following examples: (i) The report by Brauner (J. Chem. Soc., 65 (1894) 393) that pyrolysis of K.sub.3 PbF.sub.7 yields F.sub.2 was refuted by Ruff (Z.anorg. allgem.Chem., 98 (1916) 27,38); and (ii) the thermal decompositions of CoF.sub.3 (NSWC Report WOL TR 77-23) and K.sub.2 NiF.sub.6.KF (J. Fluorine Chem., 7 (1976) 359) require impractically high temperatures and are based on equilibrium reactions which at lower temperatures result in a reformation of the starting materials under fluorine uptake. Consequently, none of these systems are useful for PCL applications which require a solid grain gas generator fulfilling the following conditions: (1) generation of pure fluorine to avoid buildup of gases which deactivated the laser; (2) generation of F.sub.2 at high pressure to minimize the size of the gas accumulator and to permit feeding of an atmospheric pressure laser; (3) generation of F.sub.2 at moderate temperatures to avoid metal fires in the generator and fluorine losses to the hardware, to minimize the energy requirements for the generator, and to obtain a fast generator response time; and (4) the F.sub.2 generating reaction must be irreversible to eliminate the need for either continuous heating of the generator or complex hardware allowing rapid removal of the F.sub.2 while the generator is hot.